External IPv6 address remains reachable

external IPv6 address (home.nono.com) was unreachable
from outside because the local Comcast router wasn't
able to discover it because my firewall rule was
blocking neighbor-solicitation sent to multicast
address ff02::1/16.  Now external address accepts
all appropriate ICMP6 types whether sent to local
interface's address or to the multicast address

ff02::1/16 is "All nodes on the local network segment"

https://en.wikipedia.org/wiki/Multicast_address

ff02::1